In an exhaust gas recirculation system for an internal combustion engine, a part of the exhaust gas mass flow flowing through the exhaust gas manifold is recirculated into the intake plenum of the engine. The recirculated exhaust gas is mixed with fresh air in or before the intake plenum. The exhaust gas recirculation rate, i.e. the proportion of the exhaust gas mass flow in the total flow of the exhaust gas/fresh air mixture supplied to the intake plenum, may be adjusted via one or more valves and possibly also via the turbine geometry of a turbocharger having a variable turbine geometry. In vehicles with turbochargers, the exhaust gas is frequently taken off from the exhaust system upstream of the turbine section of the turbo charger.
One goal to be achieved through the use of exhaust gas recirculation systems is the reduction of the pollutant discharge from engines. This requires suitable control systems for the exhaust gas recirculation system. An exhaust gas recirculation system in which the exhaust gas recirculation rate is adjusted on the basis of the operating state of the internal combustion engine is described in U.S. Pat. No. 5,927,075.
To further improve the behavior of internal combustion engines with exhaust gas recirculation in regard to their pollutant discharge, an exhaust gas recirculation system in which a pressure-dependent regulation of the exhaust gas recirculation rate takes place is described in DE 101 30 471 A1.
The inventors herein have recognized that, although it has already been possible to achieve advances in reducing the pollutant emissions through the use of exhaust gas recirculation systems of the prior art, further improvements are required. For example, in the exhaust gas recirculation systems of the prior art, a strongly pulsating flow of the exhaust gas recirculation can occur, for example. The strong pulsating leads to a poorer quality of the mixing of exhaust gas and fresh air and thus to a non-optimal behavior with regard to the pollutant discharge. In addition, it is difficult to measure the mass flow of the recirculated exhaust gas in exhaust gas recirculation systems of the prior art.
Further, a strong interaction between the dynamics of exhaust gas recirculation and the dynamics of the charging pressure in the exhaust gas turbocharger leads to problems in the application of conventional decentralized control algorithms for controlling the exhaust gas mass flow or the charging pressure, respectively.
Finally, the temperature in the intake plenum depends on the charging pressure and the exhaust gas mass flow and can thus not be adjusted independently of these two parameters.
Accordingly, the present invention is directed to a method and a system to provide a motor vehicle with an improved exhaust gas recirculation system, and more particularly to an improved method for adjusting the exhaust gas recirculation rate in an exhaust gas recirculation system.
According to this invention, an exhaust gas recirculation system for an internal combustion engine having an intake plenum, an exhaust gas system, and a fresh-air feed line connected to the intake plenum includes: an exhaust gas recirculation line connected to the intake plenum, at least one sensor, arranged in the intake plenum, said sensor providing a signal indicative of an amount of an exhaust gas component, a controller reading said sensor signal, said controller calculating a correcting variable based on said sensor signal, and adjusting a mixing ratio of exhaust gas to fresh air in the intake plenum based on said calculated correcting variable.
According to one aspect of the invention, the sensor is a gas concentration sensor. In one embodiment of the present invention, the sensor determines the oxygen concentration in the intake plenum and to outputs a variable representing the oxygen concentration to the controller. In an alternative embodiment, the sensor may be a carbon monoxide sensor.
The exhaust gas recirculation system according to the invention enables the oxygen concentration or carbon dioxide concentration in the intake plenum to be estimated, which makes it possible to control the percentage by mass of the inert gas in the intake plenum.
Instead of on the basis of the oxygen or carbon dioxide concentration measured in the intake plenum alone, the correcting variable can also be produced on the basis of the oxygen or carbon dioxide concentration measured/estimated in the intake plenum together with an oxygen or carbon dioxide concentration measured in the exhaust gas system. In this case, the exhaust gas recirculation system is also equipped with a gas concentration sensor for detecting the oxygen concentration or carbon dioxide concentration, which is arranged in the exhaust gas system, for example in the exhaust manifold.
A turbocharger with variable turbine geometry and/or an exhaust gas return valve in the exhaust gas recirculation line and/or a choke valve in the fresh air feed line can be used for adjusting the mixing ratio of exhaust gas to fresh air. Correspondingly, the exhaust gas recirculation system according to the invention is equipped with an exhaust gas return valve in the exhaust gas recirculation line and an actuator for influencing the valve position of the exhaust gas return valve in one embodiment of the invention. Alternatively or additionally, the exhaust gas recirculation system according to the invention can be equipped with a turbocharger with variable turbine geometry and an actuator for influencing the turbine geometry. As a further alternative or also additionally, the exhaust gas recirculation system according to the invention can have a choke valve in the fresh-air feed line and an actuator for influencing the valve position of the choke valve.
The invention is suitable for use in exhaust gas recirculation systems with high-pressure exhaust gas recirculation lines and systems with low-pressure exhaust gas recirculation lines. Naturally, the invention can also be used in exhaust gas recirculation systems which are equipped both with a high-pressure exhaust gas recirculation line and with a low-pressure exhaust gas recirculation line.
In yet another embodiment of the present invention, a method for controlling the mixing ratio of exhaust gas to fresh air in an exhaust gas recirculation system of an internal combustion engine, includes: measuring an amount of an exhaust gas component in an engine intake plenum, calculating a correcting variable based on said measured exhaust gas component amount, and adjusting a mixing ratio of exhaust gas to fresh air in said intake plenum based on said received correcting variable. The sensor may be an oxygen sensor or a carbon monoxide sensor.
The method according to the invention makes it possible to keep the mixing ratio in the intake plenum in a stable, steady-state condition.
The control method can be improved further, in particular with respect to transitions between various operating states of the engine, if the open cross-sectional area of the exhaust gas return valve, which is available to the exhaust gas mass flow to be recirculated, is known with sufficient accuracy. For this purpose, the method can comprise a measurement of this effective cross-sectional area which is available.
The above advantages and other advantages, and features of the present invention will be readily apparent from the following detailed description of the preferred embodiments when taken in connection with the accompanying drawings, and from the claims.